1. Field of the Invention
The present invention relates to a centrifugal blood pump used For heart-lung machines or the like.
2. Prior Arts
Conventionally, pulsatile pumps and roller pumps were used as blood circulation pumps for heart-lung machines or the like. In recent years, centrifugal pumps which are compact, efficient and reliable have become to be used widely.
However, centrifugal blood pumps are apt to cause the problem of generating thrombi at bearings and sealing parts because of blood stagnation around the sealing parts for sealing the rotation axis of the impeller with vanes and heat generation in the sealing parts. In addition, there is the danger of leaking blood through the sealing parts. Because of these problems, the pumps cannot be operated continuously for an extended period of time.
To solve these problems, various centrifugal blood pumps have been proposed, which require no seals for the rotation shaft.
In the case of the blood pump described in the specification of U.S. Pat No. 4,688,988, the impeller with vanes accommodated in the casing of the pump is equipped with magnets which form a part of a magnetic suspension means and magnets which form a part of a magnetic rotation means. Outside the casing, the pump is equipped with an electric magnet means disposed corresponding to the magnets of the impeller. By operating these electric magnet means, the impeller in the casing is suspended in the normal position and rotated properly. With this type of pump, however, it is difficult to control the position and suspension conditions of the impeller with vanes, causing unstable impeller rotation. Furthermore, the pump becomes complicated and large, confronting difficulty when it is put to practical use.
In the case of the blood pump described in the specification of U.S. Pat. No. 4,984,972, the boss located in the center of the impeller is mounted on the bearing supported in the pump chamber inside the housing of the disposable pumping unit of the pump, for example, the bearing formed at the top section of the conical stator of the pump, to support the impeller, and the magnets disposed around the impeller are combined magnetically to rotate the impeller and the magnetic drive means disposed outside the pumping unit. Since the impeller of this pump is supported only at a single point and the magnets are carried on the impeller, it is difficult to balance the impeller, causing unstable rotation.
In the case of the centrifugal blood pump described in the specification of U.S. Pat. No. 4,507,048, the nearly conical impeller with vanes of the pump, rotatably accommodated in the casing, is supported by the watch-type jewelled pivots formed at the upper and lower ends of the center axis thereof. On the bottom surface side of the conical impeller, a magnetic means is disposed and cooperates with the magnetic drive means disposed outside the casing to rotate the impeller. Since the center axis of the impeller of this pump is supported by the two upper and lower jewelled pivots, the impeller's dynamic balance of the pump is better than that of the pump described in the above-mentioned U.S. Pat. No. 4,984,972, ensuring stable rotation of the impeller. However, since this pump has magnets on the bottom surface of the conical impeller, it is necessary to reduce the gap between the bottom surface of the impeller and the casing to enhance the efficiency of impeller rotation obtained by the cooperation of the magnets and the magnet drive means outside the casing. As a result of reducing the gap, it is difficult for blood to flow through the gap, thereby being apt to cause a problem of generation of thrombi, particularly at the jewelled pivot on the bottom surface side of the impeller.
As described above, the centrifugal blood pumps having been proposed so far without using shut-off seals had various problems and could not be put to practical use.